The Audio/Color PCB is so named because it contains not only the circuitry required to generate all sounds, but also the color selection decoding circuitry and video output connector.
This PCB contains a dedicated 6502 microprocessor and circuitry to support the simultaneous generation of many types of sound, including three channel music. The Logic PCB simply sends commands to the Audio/Color PCB via a bi-directional communications port and the Audio/Color PCB takes it f rom there. In some cases this PCB even aids the Logic PCB in some of it's calculations when there is not enough processing time available on the Logic PCB.
As a result of this structure, the actual program to generate sounds or music resides on the Audio/Color PCB. There is also a handshake required between the two PCB's in order for the system to power up correctly, and of course, there is no video output without the Audio/Color PCB connected.
1. Logic and Power Interface (P5,J2,J3)
Connector P5 provides the audio/color PCB with all the power it requires to operate. Also fed through this connector are the two speaker output leads. P5 interfaces only to the power supply module and the speaker, through the main harness.
Connectors J2 and J3 are the most significant path of communication between the Logic and Audio/Color PCB's. Address lines, Bi-directional Data lines, processor control li nes, and the Audio/Color PCB Select line are all passed through these two connectors.
2. Communications and Address Decoding (9B,13D)
Peripheral Interface Adapter (PIA) 9B, in concert with 8B (another PIA ,shown on page two) serves as a bi-directional communications path between the Logic PCB and the Audio/Color PCB. During information transfer between the two PCB's, both PIA's are in use. Information from the Logic PCB microprocessor passes through the PIA at 9B to the PIA at 8B, then to the microprocessor on the Audio/Color PCB. When information is passed the other direction, the path is the same, but the direction is reversed.
During the time that no information transfer is occurring between the two PCB's, both microprocessors can continue to operate independently.
Also shown on page one is 13D, a 3-line to 8-line decoder, used to generate the write signals for the Color Data Latches. These Latches will be covered in the text for page five of the Audio/Color PCB.
1_. 6502 Microprocessor (3B)
This microprocessor is the same as that used on the Logic PCB, but is exclusively dedicated to the generation of sound. It can communicate with the Logic PCB microprocessor, and receives it's instructions thereby. Once it has received it's instructions, however, it asserts complete control over all Audio/Color PCB circuitry and ignores the Logic PCB microprocessor until such time as it is informed that another command is ready. Some commands are of a type that must be processed immediately, irregardless of other operations in progress, and some commands can wait until the operations in progress are completed. The program on the Audio/-Color PCB handles all these eventualities appropriately.
2. Peripheral Interface Adapters (8B, 7B)
The PIA at 8B, as mentioned in the text for page one, is used in bi-directional communications between the microprocessors on the Logic PCB and the Audio/Color PCB.
The PIA at 7B is used for two fundamental purposes on this PCB. The first, and most important, is that it contains the RAM that the microprocessor uses for zero page and stack operations. The PIA only contains 128 bytes of RAM, which under normal circumstances would not be sufficient for both zero page and stack. In this case, however, the memory map on this PCB has been altered, so that when the microprocessor thinks it is putting the stack at address 01FFH it is actually putting it at address 007FH.
The second use of this device is that of a programmable interval timer, used for various purposes unique to the specific sounds being generated on this game. The ability of this device to generate interrupts at time out is utilized here.
3. Address Decoding (4B)
Keyboard Encoder (4B) is used here to generate the chip selects of all devices located in the memory map of the Audio/Color PCB.
4. Music Generator (2B)
Another Programmable Counter/Timer device is used here to generate music (and sometimes other special effects) in up to three channels (or voices) simultaneously. The music is created by a special software operating system, and all but the counter/timer chip is therefore invisible.
5. Master Oscillator (A1,B1)
This oscillator is the source of all timing on the Audio/Color PCB. If this clock stops running, so does everything else on the Audio/Color PCB. It is, however, completely independent of the clock and other timing signals generated by the Master Oscillator located on the Logic PCB.
6. Program Memory (3A,4A,5A,6A,7A)
The memory devices used here are 2716 (2048 x 8) EPROMS. The DIP shunt located at 8A is used to reconfigure the control and power supply lines, if necessary, for equivalent devices from different manufacturers, whose pinouts may not be the same.
7' Output Filter Latch (1C)
This latch is used simply to switch different output filter capacitors in or out of the circuit to soften or shade the sound, according to program requirements, or to change the volume.
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